Comparative Gas‐Brine Relative Permeability of H ₂ , N ₂ , and CO ₂ Under Subsurface Storage Conditions

Gas‐brine relative permeability controls subsurface gas storage, including underground hydrogen and CO 2 storage. Here, we measure steady‐state gas‐brine relative permeabilities for H 2 , N 2 , and CO 2 in a sandstone core at 0.1–6 MPa under identical conditions. A multi‐stage equilibration protocol yields reproducible relative permeability curves and isolates the effects of pressure and gas properties. Gas relative permeability increases with pressure for all three gases, strongest for CO 2 and weakest for H 2 . These variations follow a common interfacial‐tension‐based power‐law scaling that captures the endpoint gas mobility, irreducible water saturation, and crossover saturation within a unified framework, indicating that interfacial effects are the primary control on gas mobility. H 2 and N 2 behaviors diverge only at the highest pressure examined, suggesting that N 2 may serve as a practical proxy for H 2 at low to moderate pressures. The results provide quantitative constraints relevant to UHS and CCS.